The subject of the present invention are processing additives for use in the thermoplastic forming of polymers, especially on a basis of mixed polymers containing mainly vinyl chloride units. These thermoplastic compositions contain heat stabilizers from the group of the metallic soaps, metallic phenolates, organotin compounds and similar substances as well as other conventional additives that are used in this plastics technology.
A degradation of polyvinyl chloride and mixed polymers containing vinyl chloride units can easily occur at the elevated temperatures applied during the processing of the thermoplastic polymers, for example, for the manufacture of pipes, bottles, profiles and similar goods by extrusion, injection molding, blowing and similar methods. This results in undesirable discolorations and impairment of the mechanical properties. For this reason, stabilizers are added for the hot forming process that counteract such a degradation. These are, for example, lead salts of organic and/or inorganic acids, barium, cadmium, calcium, zinc and other metallic salts of fatty acids or also organotin compounds.
Frequently so-called co-stabilizers are added to such compounds that also are called primary stabilizers, to improve their effectiveness.
The heavy metal stabilizers develop an absolutely satisfactory effect in actual practice. However, there are certain objections to their use, particularly those of a toxicological nature. For this reason, efforts have been made for a long time to substitute less objectionable substances for the conventional heavy metal stabilizers. To accomplish this the heavy metal stabilizers have been replaced by soaps of the lighter alkaline earth metals, preferably calcium soap, which is supplemented with additions of zinc soap, imino compounds and epoxy compounds, if desired.
The stabilizing effect of the calcium soap system is relatively weak in comparison with that of the heavy metal compounds. Consequently, the range of application has been quite limited so far for such stabilizer systems.